1. Field of the Invention
The invention relates to a memory circuit and to a method for reading out a specific item of operating information contained in a memory circuit.
2. Description of the Related Art
In memory circuits, in particular in SDRAM (synchronous dynamic random access memory), internal product-specific data, for example the maximum operating frequency at which the memory circuit can be operated, the bus width, other optional features supported etc., are present in the memory circuit. This data cannot be read out by a memory controller that usually drives the memory circuit. This is due to the fact that the memory circuit merely has configuration registers (mode registers, extended mode registers), to which configuration data can be written, for the purpose of controlling its operation, and there is otherwise no interface or drive command (in accordance with a specification) which can be used to read out the internal product-specific data from these configuration registers.
Dynamic memory circuits, for example the SDRAM, can usually be driven using eight different drive commands which are coded with the aid of three command (control) signals. These drive commands are sufficient for normal operation of the SDRAM. However, these eight drive commands do not include a drive command for reading out internal product-specific data.
However, it is desirable, for optimized operation of the memory controller, to read out the product-specific data from the memory circuit in the form of operating information. The memory controller could thus, for example, inquire whether or not a particular memory circuit comprises a particular optional feature, for example a temperature sensor. The memory controller could then configure itself and the memory circuit in an appropriate manner on the basis of the presence of the feature.
Providing a further command for reading out the specific operating information would require the provision of a further command signal that would have to be provided using a further connection pin of the memory circuit. It has hitherto been possible, in memory circuits which are combined to form memory modules, to provide such data, for example, in a separate non-volatile memory chip that has an appropriate interface. Such a memory chip is programmed in accordance with the memory circuits used, but errors can occur if the programming does not correspond to the features of the corresponding memory circuits.
However, there is no such option in memory circuits which are used individually. In this case, the corresponding operating information required must be taken from the data sheet for the memory circuit and permanently prescribed to the memory controller.
Therefore, it is an object of the present invention to provide a memory circuit in which the specific operating information can be read out in a simple manner, in particular without having to provide additional connections or command signals. It is furthermore an object of the present invention to provide a method for reading out a specific item of operating information contained in a memory circuit.